Nitrogen-doped epitaxial graphene grown on SiC(000?1) was prepared by exposing the surface to an atomic nitrogen flux. Using Scanning Tunneling Microscopy (STM) and Spectroscopy (STS), supported by Density Functional Theory (DFT) calculations, the simple substitution of carbon by nitrogen atoms has been identified as the most common doping configuration. High-resolution images reveal a reduction of local charge density on top of the nitrogen atoms, indicating a charge transfer to the neighboring carbon atoms. For the first time, local STS spectra clearly evidenced the energy levels associated with the chemical doping by nitrogen, localized in the conduction band. Various other nitrogen-related defects have been observed. The bias dependence of their topographic signatures demonstrates the presence of structural configurations more complex than substitution as well as hole-doping.
@article{arxiv.1204.3560,
title = {Localized state and charge transfer in nitrogen-doped graphene},
author = {Frederic Joucken and Yann Tison and Jerome Lagoute and Jacques Dumont and Damien Cabosart and Bing Zheng and Vincent Repain and Cyril Chacon and Yann Girard and Andres Rafael Botello-Mendez and Sylvie Rousset and Robert Sporken and Jean-Christophe Charlier and Luc Henrard},
journal= {arXiv preprint arXiv:1204.3560},
year = {2016}
}